mon/PGMap: OSD byte counts 4x too large (conversion to bytes overzealous)

Fixes: #6049
Signed-off-by: Dan Mick <dan.mick@inktank.com>
Merge pull request #517 from dmick/wip-6049

mon/PGMap: OSD byte counts 4x too large (conversion to bytes overzealous)

Reviewed-by: Joao Eduardo Luis <joao.luis@inktank.com>